How to send alert or message from view.py to template?

if request.method == 'POST' and request.FILES:
.
--code to verify and save the file or generate error msg--
.
if error != 'false':
    return JsonResponse({'msg': error)

$.ajax({ 
        url: 'foo', 
        type: 'post', 
        data: bar, // sending file here
        contentType: false, 
        processData: false,
        async: true,
        success: function(data){ 
            if(data === null){
                alert('success')
            }else {
                alert(data.msg); // can use JS to display the error near the upload field
            }
        },
    });